docs: def _convert(self, image, output=None):
          """Private method for converting a single PNG image to a PDF."""
          with Image.open(image) as im:
              width, height = im.size
  
              co = CanvasObjects()
              co.add(CanvasImg(image, 1.0, w=width, h=height))
  
              return WatermarkDraw(co, tempdir=self.tempdir, pagesize=(width, height)).write(output)